import java.util.Scanner;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 23735
 * Date: 2023-09-27
 * Time: 22:27
 */
public class Solution {

    /**
     *  贪心, 挨个判断, 如果是 0, 那么就将它 右边, 下边的两个位置置为 -1, 表示不能放
     *  为什么是右边和下边 ? 因为是从左到右从上到下挨个判断的, 所以只用考虑右边和下边即可
     *  判断的过程中记录 0 的个数即可
     * @param args
     */
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNextInt()) {
            int col = in.nextInt();
            int row = in.nextInt();
            int[][] arr = new int[row][col];
            int count = 0;
            for (int i = 0; i < row; i++) {
                for (int j = 0; j < col; j++) {
                    if (arr[i][j] == 0) {
                        count++;
                        if (j + 2 < col) {
                            arr[i][j+2] = -1;
                        }
                        if (i + 2 < row) {
                            arr[i+2][j] = -1;
                        }
                    }
                }
            }
            System.out.println(count);
        }
    }
}
